1. Field of the Invention
The present invention relates to a two-stage supercharging exhaust turbocharger including a high-pressure-stage supercharger driven by exhaust gas discharged from an exhaust manifold of an engine; a low-pressure-stage supercharger driven by the exhaust gas used to drive the high-pressure-stage supercharger, the high-pressure-stage supercharger and the low-pressure-stage supercharger being arranged in series in an exhaust gas passageway; and an exhaust gas control valve configured to selectively change flow rates of the exhaust gas passageways of the high-pressure-stage supercharger and the low-pressure-stage supercharger.
2. Description of the Related Art
In recent years, a vehicle diesel engine adopts a two-stage supercharging exhaust turbocharger which includes a high-pressure-stage supercharger having a high-pressure turbine driven by exhaust gas discharged from an engine and a low-pressure-stage supercharger having a low-pressure turbine driven by the exhaust gas used to drive the high-pressure-stage supercharger, wherein the high-pressure-stage supercharger and the low-pressure-stage supercharger are arranged in series in an exhaust gas passageway, and wherein air subjected to a first-stage pressurizing operation of the low-pressure compressor of the low-pressure-stage supercharger is subjected to a second-stage pressurizing operation of the high-pressure compressor of the high-pressure-stage supercharger and is supplied to an engine.
In the engine provided with the multi-stage supercharging exhaust turbocharger, a two-stage supercharging operation using both the high-pressure-stage supercharger and the low-pressure-stage supercharger is carried out in a low-speed running region, which is advantageous in a transient characteristic and an increase of low-speed torque of the engine. Additionally, a one-stage supercharging operation using the low-pressure-stage supercharger is carried out in a high-speed running region of the engine by allowing the exhaust gas to bypass the high-pressure-stage supercharger. In this manner, it is possible to further improve efficiency of the compressor and thus to realize a reliable running state having an excellent degree of freedom in matching.
FIG. 6 is an explanatory view showing an operation of the two-stage supercharging exhaust turbocharger.
In FIG. 6, Reference Numeral 1 denotes a high-pressure-stage supercharger, where the high-pressure-stage supercharger 1 includes a high-pressure turbine 1a and a high-pressure compressor 1b coaxially driven by the high-pressure turbine 1a. Reference Numeral 2 denotes a low-pressure-stage supercharger, where the low-pressure-stage supercharger 2 includes a low-pressure turbine 2a and a low-pressure compressor 2b coaxially driven by the low-pressure turbine 2a. 
The exhaust gas discharged from a cylinder 100 of the engine is collected in an exhaust manifold 103 and is supplied to the high-pressure turbine 1a of the high-pressure-stage supercharger 1 via an exhaust pipe 4. A part of the exhaust gas is supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 via an exhaust gas control valve 5, an exhaust pipe 6, and an exhaust pipe 10.
Here, the exhaust gas control valve 5 shown in a Y part of FIG. 6 is provided between the high-pressure-stage supercharger 1 and the low-pressure-stage supercharger 2, and is used to control a relationship between an amount of the exhaust gas of the high-pressure-stage supercharger 1 and an amount of the exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 by controlling an opening degree thereof. That is, the exhaust gas passing through the high-pressure turbine 1a of the high-pressure-stage supercharger 1 and an exhaust pipe 8 and the exhaust gas of which a flow rate is controlled by the exhaust gas control valve 5 are mixed at an exhaust pipe 9 and the mixed gas is supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2 via an exhaust pipe 10.
In the low-pressure-stage supercharger 2, the low-pressure compressor 2b is coaxially driven by the low-pressure turbine 2a so as to pressurize air supplied from an air cooler 2c, and the pressurized air is supplied to the high-pressure compressor 1b of the high-pressure-stage supercharger 1 via an air supply pipe 21 and an air supply suction pipe 18.
In the high-pressure-stage supercharger 1, the high-pressure compressor 1b is coaxially driven by the high-pressure turbine 1a so as to supply the pressurized air to a cylinder 100 of an engine via an air supply pipe 20, an intercooler 2d, an air supply pipe 22, and an exhaust manifold 101.
Here, a compressor bypass valve unit 05 is provided in a bypass pipe 17 of the high-pressure compressor 1b so as to control an amount of air bypassing the high-pressure compressor 1b. 
Additionally, a waste gate valve 12 is provided in a bypass pipe 11 of the low-pressure turbine 2a so as to control an amount of exhaust gas bypassing the low-pressure turbine 2a. 
FIG. 4 is an explanatory view showing a structure of a main part of the two-stage supercharging exhaust turbocharger.
In FIG. 4, Reference Numeral 1 denotes a high-pressure-stage supercharger, where the high-pressure-stage supercharger 1 includes a high-pressure turbine 1a and a high-pressure compressor 1b coaxially driven by the high-pressure turbine 1a. Reference Numeral 2 denotes a low-pressure-stage supercharger, where the low-pressure-stage supercharger 2 includes a low-pressure turbine 2a and a low-pressure compressor 2b coaxially driven by the low-pressure turbine 2a. 
An outlet of the high-pressure turbine 1a (not shown in FIG. 4) is connected to a low-pressure connection casing 12 at a connection surface 11a by the use of bolts so as to be connected to a low-pressure gas inlet passageway 2s of the low-pressure-stage supercharger 2 via the low-pressure connection casing 12.
The compressed air discharged from the low-pressure compressor 2b of the low-pressure-stage supercharger 2 is sucked into the high-pressure compressor 1b of the high-pressure-stage supercharger 1 via an air supply connection pipe 21 and a high-pressure compressor cover 9. Here, as described above, a compressor bypass valve unit 05 is provided in a bypass pipe 17 of the high-pressure compressor 1b so as to control an amount of air bypassing the high-pressure compressor 1b and discharged from an air discharge pipe 18.
FIG. 5A is a view showing a structure of a low-pressure connection portion and an exhaust manifold portion of the two-stage supercharging exhaust turbocharger shown in FIG. 4, and FIG. 5B is a sectional view taken along the line Z-Z shown in FIG. 5A.
In FIG. 5, Reference Numeral 200 denotes an exhaust manifold portion, where the exhaust manifold 103 is integrally formed with a housing 10 of the high-pressure turbine 1a of the high-pressure-stage supercharger 1 by casting.
Reference Numeral 103a denotes an exhaust gas inlet flange of each cylinder (not shown) of the engine. As shown in FIG. 5, a right angle is formed between a flange surface of the exhaust gas inlet flange 103a and a flange surface 1z of the high-pressure housing 10, and the flange surface is coupled to an exhaust gas outlet flange (not shown) of each cylinder by the use of a plurality of bolts.
As shown in FIG. 5B, Reference Numeral 201 denotes a low-pressure connection portion. The low-pressure connection casing 12 is provided with the exhaust gas control valve 5 and is integrally formed with an EGR pipe 15.
The exhaust gas control valve 5 provided between the high-pressure-stage supercharger 1 and the low-pressure-stage supercharger 2 controls an opening degree thereof so as to control a relationship between an amount of the exhaust gas of the high-pressure-stage supercharger 1 and an amount of the exhaust gas bypassing the high-pressure-stage supercharger 1 and supplied to the low-pressure turbine 2a of the low-pressure-stage supercharger 2.
That is, in FIG. 5B, the exhaust gas control valve 5 includes a valve member 54 and a valve seat 55 on which the valve member 54 is seated, where one end of the valve member 54 is supported to a rotary shaft 52 so as to be rotatable about a shaft center 52a of the rotary shaft 52 in a direction indicated by the arrow W in terms of a support arm 56.
The lower surface 54a of the valve member 54 is formed into a plane. When the valve member 54 is swung about the shaft center 52a of the rotary shaft 52, a lower surface 54a of the valve member 54 comes into contact with a seat surface 55a of the valve seat 55 to thereby close the valve member 54.
Upon opening the valve member 54, the rotary shaft 52 is rotated in a direction indicated by the arrow W of FIG. 5 by the use of an exhaust gas control valve driving unit (not shown) to thereby open the valve member 54 in terms of the support arm 56.
Then, the exhaust manifold portion 200 with the above-described configuration and the low-pressure connection portion 201 equipped with the exhaust gas control valve 5 are connected to each other at the connection surface 11a by the use of a plurality of bolts.
Additionally, Patent Document 1 (Japanese Utility Model Application Laid-Open No. H06-48119) discloses a two-stage exhaust turbocharger in which a high-pressure-stage supercharger and a low-pressure-stage supercharger are connected to each other in terms of a low-pressure connection pipe, an exhaust gas control valve is provided in an inlet of the low-pressure-stage supercharger, and then a part of exhaust gas in the inlet of the low-pressure-stage supercharger is returned to an exhaust manifold.
In order to install an engine equipped with the two-stage supercharging exhaust turbocharger in a narrow engine room of a vehicle engine, an installation space in the engine room increases inevitably since the two-stage supercharging exhaust turbocharger is larger than a single-stage supercharging exhaust turbocharger.
For this reason, it is required to efficiently install the engine equipped with the two-stage supercharging exhaust turbocharger in the narrow engine room by realizing a compact in size of the structure of the two-stage supercharging exhaust turbocharger to decrease the installation space thereof as small as possible.
In the exhaust manifold portion 200 according to the convention art shown in FIG. 5, the exhaust manifold 103 is integrally formed with the housing 10 of the high-pressure turbine 1a of the high-pressure-stage supercharger 1 by casting. In the low-pressure connection portion 201, the low-pressure connection casing 12 is provided with the exhaust gas control valve 5 and is integrally formed with the EGR pipe 15. The exhaust manifold portion 200 and the low-pressure connection portion 201 are connected to each other at the connection surface 11a by the use of the plurality of bolts.
For this reason, since it is necessary to provide two components, that is, the exhaust manifold portion 200 and the low-pressure connection portion 201, the number of components increases and the number of assembling processes using a bolt increases. Also, it is necessary to carry out many processes upon separating the exhaust manifold portion 200 and the low-pressure connection portion 201 in the narrow engine room.
Additionally, as described above, since it is necessary to provide two components, that is, the exhaust manifold portion 200 and the low-pressure connection portion 201, the weight of the assembling components increases.